Recent awareness that environmental factors, particularly those related to diet, may play an important role in the development of obesity in both man and animals, has led to increasing interest in models of dietary-induced obesity. Work in this and other laboratories has shown that allowing rats access to a palatale sugar solution and nutritionally complete diet leads to the development of obesity. Animals maintained on this dietary regime consume more energy and are more metabolically efficient than animals given only the complete diet. The research in this proposal will investigate in more detail the importance of excess caloric intake and sugar consumption to the development of obesity and diet-induced thermogenesis (DIT). One of the aims of this proposal is to explore the possibility that the different monosaccharide components of sucrose may have different effects on lipogenesis. We will test the hypothesis that fructose stimulates lipogenesis in white adipose tissue, while glucose excerts a greater effect on brown adipose tissue (BAT). We propose that the mediating mechanism in sucrose-induced obesity is insulin. It is hypothesized that manipulations which elevate insulin levels will be associated with increased metabolic efficiency and obesity, while those that decrease insulin will attenuate the development of sucrose-induced obesity. It has been hypothesized that the increase in the percentage of sugar in the American diet over the past several decades has contributed to the increased prevalence of obesity also seen during this period. Thus our model of sucrose-induced obesity may be very appropriate for human obesity, as sugar is frequently consumed as a single nutrient source.